Last month Mobius asked a question about a world where time can flow both forward and backward. I suggested a particular solution to the problem he was looking at, and I would like to open up a follow up question as part of the fortnightly challenge.
The world of two streams
In the world I am looking at, time flows in two counterflowing "streams" with eddies connecting them. In the "live" stream, we see physics like usual. Quantum mechanics, general relativity, take your pick from modern science, we see these behaviors in this stream. The other stream is the "dead" stream, and it is where we go when we die. The physics of this stream will be constrained shortly, but the most important trait of this stream is that entities within this stream travel in the opposite direction of time. Any entity can enter this reversed stream simply by dying. Any entity within the dead stream may re-enter the "live" stream at any point [in the past] that they please, simply by wishing it so when they get there.
The physics of the dead stream are open for interpretation, but they are constrained in a way that guarantees consistency. The dead stream is ruled by knowledge and information. As you travel back in time along the dead stream, you are obliged by the natural laws to forget enough information such that, if you return to the world of the living, you have forgotten too much information to allow you to force a paradox to occur. For example, if you traveled back in time to kill your grandfather, you may be forced to forget your own last name. Or you might be forced to forget that you wanted to kill them. Or you might simply forget a key detail of your grandfather's personality that allows him to dodge the murder attempt at the last moment.
Feel free to set the rules for this forgetfulness in any way that supports your answer, with one caveat. The forgetting occurs inside the dead realm, not in the transition from dead to alive. The dead must constantly be forgetting enough to ensure that they have no opportunity to create a paradox. If they avoid a "cusp" where a paradox could have occurred, but they elected not to cross back over to the living at that point, they still have forgotten the information that could have been used to cause a paradox. The universe is overcautious in that respect.
This also means that the path one takes in the dead stream matters. If one chooses to observe cusp after cusp before arriving at a location, they may have had to forget more than if one chooses to sidestep cusps entirely, arriving at the same location. A dead entity which wishes to avoid forgetting would be wise to avoid sensitive areas of spacetime on its trip backwards through time.
Religion of two streams
For this question, I am looking for what traits we would see in religions which are not seen in our simpler unidirectional "arrow of time" approach used in the modern world today. Consider that a dying individual could travel back in time so far as to get "lost," forgetting all that made that entity an individual (but a Buddha, which theoretically knows only eternally true facts, could travel backwards forever without change). Self interaction is allowed in this world, so a religious individual could go back in time to teach his or her younger self, as long as that teaching did not invoke a causality paradox (if it would invoke such a paradox, the older version would simply find that they forgot too many details to cause the paradox). Obviously, in this world, life after death is a known thing, but there might be whispers of a "true death" that goes beyond simply entering the dead stream.
What traits would be found in religions of this world?
- I am interested in traits of religion which do not tend to appear in our world. I am looking for traits which are specialized to this particular universal structure. At the very least, if the trait exists in our world's religions too, the structure of this universe should dramatically amplify its importance.
- The best answers are those which demonstrate a religious trait so profound that its mere presence will shape the world we build around a character. I'm looking for something that changes the world, not something which can be kept isolated inside a monastery.
- The physics of the dead stream are open for interpretation. However, the universe should support a dualist viewpoint: in the live stream, body and mind/soul are attached. Moving to the dead stream separates the body and mind/soul, allowing the mind/soul to move backwards. (You are free to define a physical version of the dead stream, if you so prefer, but I should be able to treat the answer as though there was a separation between body and mind/soul, and you'll have to ensure information theory proves that your world prevents paradoxes)
- The effect of a mind/soul trying to enter the living world in a location where there is no body for it to inhabit are up to you. It could be a "true death," or it could turn you into a ghost to haunt for all time. You might possess someone nearby, or you might simply enqueue to be given the "next available body nearby." Feel free to use imagination if it helps build your story for the religious traits offered as your answer.
- Small and profound is better. It is best if a single trait explains multiple facets of people's world-view within a world. To use the example I already gave, one can define Nirvana within Buddhism within this particular universe. That definition also starts to define "ghosts," in that they are souls that forgot who they are along the way.
- I expect the religious traits to be very dependent on how the universe goes about choosing what information the dead forget. Do not be afraid to specify details about this process. Just make sure that those details do not leave loopholes which would allow paradoxes to occur.
- Answers should leverage the atypical nature of the dead stream. Obviously any solution along the lines of Novikov's self-consistency principle can trivially be proven to meet these rules, but they are well explored answers and lead to less interesting outcomes. Novikov started from the assumption that the physics of spacetime which contains spacetime loops is identical to that of physics of normal spacetime (that which has no loops). I am explicitly starting from the assumption that there are regions where the physics differs in some portions of the loops.
EDIT: There was a question about what form dead mind/souls return to the world of the living in. The answer is up to you. The intent is to allow one of these souls to "recycle" into a newborn baby body (at the moment of ensourcelement), thus providing the mind/soul with a new body to use. However, to avoid over-specifying the system, I allow the dead to return at any time and place. This may turn them in to ghosts or shadows, or it may simply scatter their mind across all space time. It could also lead to superstitions like saying "bless you" after the sneeze. The origin of that ritual is that it was believed a demon could sneak in up your nose after you sneeze. Perhaps that myth is not as far from the truth as we think today. Perhaps you drop your guard when you sneeze, giving a dead mind/soul an opportunity to partially hijack a fully grown body.